The recognition of polymorphonuclear leukocyte (PMN) asialo- or sialoglycoconjugate receptors by the Gal/GalNAc reactive fimbrial lectin of A. viscosus T14V or the sialic acid reactive lectin of S. gordonii DL1, respectively, resulted in phagocytosis, production of superoxide anions and release of the contents of secondary PMN granules. However, only phagocytosis initiated by the actinomyces lectin was accompanied by stimulation of PMN chemiluminescence and destruction of the bacteria. Putative PMN glycoprotein and glycolipid receptors for the actinomyces lectin were identified. Studies utilizing the HL60 cell line indicated that the expression of receptors for the actinomyces lectin was enhanced and processing of a glycoprotein receptor occurred during differentiation of the cells towards PMNs. Although S. gordonii DL1 remained viable following lectin mediated ingestion by PMNs, these bacteria served as vehicles for the initiation of killing of A. viscosus T14V if the two bacteria were coaggregated prior to incubation with the phagocytic cells. IgG and fragments of the third component of complement (C3) deposited on bacteria also initiated PMN dependent killing of A. viscosus T14V, but only when localized to certain bacterial surface structures. Anti-cell surface or anti-type 1 fimbriae IgGs initiated killing by PMNs but anti-type 2 fimbriae IgG was minimally effective. When IgG sensitized bacteria were incubated with complement, the localization of C3 fragments on the actinomyces was dependent on the IgG specificity. Only C3 fragments bound to the cell surface enhanced bactericidal activity. Cooperativity between the actinomyces lectin and C3 fragments was also demonstrated. Although the destruction of A. viscosus T14V could be initiated either by C3 fragments bound to the bacterial surface or by the lectin associated with the type 2 fimbriae, the bactericidal activity was enhanced more than 50 fold if the bacteria were opsonized with C3 fragments and, in addition, were incubated with PMNs in the presence of sialidase to expose the receptors for the bacterial lectin.